This invention relates to wood treatment compositions and associated methods for imparting fire retardance to wood and other cellulosic materials. More particularly, these compositions are aqueous solutions of a water soluble amide (such as urea); an oxy-acid of phosphorus (such as phosphoric acid); a metal salt of boron (such as borax); an oxy-acid of boron (such as boric acid); and a caustic material to control pH to a level of about 4.75 to about 5.25 (such as sodium hydroxide).
In recent times, more and more interest has focused upon flame retardant treatments for wood. Flame retardant treated wood is sued in a variety of ways so as to afford a greater safety to occupants of structures containing such treated wood and to consumers of wood products. Essentially, flame retardant treatments for wood and cellulosic materials fall into generally two broad categories: (1) those compositions and treatments that allow wood and cellulosic materials so treated to maintain fire performance characteristic after exposure to weather or water; and (2) those compositions and treatments that are not designed to allow wood and cellulosic materials so treated to maintain imparted fire performance or other desirable characteristics after exposure to weather or relative humidities above approximately 95%. Generally the second category of compositions are labeled as "interior use" types and represent the predominate types of wood and cellulosic treatments in today's market. These treatments are usually less expensive than treatments within the first category which are labeled as "exterior use" types.
Illustrative of various past approaches of imparting "exterior use" types of fire retardance to wood are treatment compositions disclosed in Goldstein et al., U.S. Pat. No. 2,917,408, prepared from a combination of an amide, dicyandiamide and phosphoric acid; and Goldstein et al., U.S. Pat. No. 3,159,503, prepared from a combination of dicyandiamide, phosphoric acid and formaldehyde. In Juneja, U.S. Pat. No. 3,887,511, fire retardant compositions are disclosed comprising a partially reacted mixture of urea, dicyandiamide, formaldehyde and phosphoric acid. Surdyk, U.S. Pat. No. 3,874,990, discloses a fire retardant composition comprising a combination of alkaline borate chemicals: phosphoric acid, malamine or urea and formaldehyde. Finally, Loyvet et al., U.S. Pat. No. 4,461,720 discloses a fire retardant composition prepared by first converting dicyandiamide to an aqueous guanyl urea solution. The guanyl urea solution is then methyolated and phosphoric acid is introduced in order to product a phosphate salt of the methyolated guanyl urea.
Disadvantages associated with these aforementioned pas formulations were primarily due to their use of formaldehyde, phosphoric acid and/or urea, and their ultimate pH. For example, formaldehyde may not be environmentally acceptable in some instances and phosphoric acid and urea are both known to be relatively corrosive and hygroscopic when employed in art-disclosed compositions at their art-disclosed pH ranges. The cost of the treated wood produced using these compositions is also relatively expensive.
Illustrative of various past practices for the creation of "interior use" treatment solutions are the compositions disclosed by Oberley in U.S. Pat. No. 4,373,010, in which dicyandiamide, phosphoric acid and boric acid were combined to produce a fire retardant composition. Another "interior use" type of composition, known to those with knowledge of the art, usually contains di-ammonium or mono-ammonium phosphate in combination with ammonium sulfate and zinc chloride.
Objects of the present invention include, without limitation, a fire retardant composition for wood which is generally environmentally acceptable; relatively low in toxicity; relatively non-corrosive and non-hygroscopic; which may be stored for relatively long periods of time; and which minimizes the degradation of the wood substrata or adjacent surfaces when subjected to abnormally high temperatures and high humidities.
These objects are accomplished by the use of a fire retardant composition containing an amide, an oxy-acid of phosphorus, a metal salt of boron, an oxy-acid of boron and sodium hydroxide, while employing a pH range of about 4.75 to 5.25.
In accordance with the present invention various preferred operative ranges associated with the components of the composition have been determined. It has been found that the amount of the amide contained within the composition of this invention may vary between about 10% to about 40%, by weight, of the total weight of the final treatment composition. Typically, it is preferred that about 28% to about 38% of the total weight of the composition is formed with an amide, with the preferred embodiment having a composition of about 33%. It has further been found that the amount of the oxy-acid of phosphorus contained within the composition of this invention may vary between about 15% to about 50% (by weight) of the total composition weight. It is preferred that the oxy-acid of phosphorus represent between about 22% to 32% of the composition, with the preferred embodiment having a composition of about 27%. Further, it has been found that the composition may contain an amount varying between about 1% to about 50% of the total composition weight, of an oxy-acid of boron and a metal salt of boron. It is preferred that the composition contain between about 10.5% and 20.5% of an oxy-acid of boron and between about 10.5% and 20.5% of a metal salt of boron, with the preferred embodiment having 15.5% of each of the boron compounds. Additionally, sodium hydroxide is contained within the composition in varying amounts of between 6.5% and 10.5% of the total composition weight. Ideally, the preferred amount of sodium hydroxide will be about 8.5% of the total composition weight.
These and other objects and advantages are attained by the invention and will become more fully apparent from the following description, taken in conjunction with specific examples included for the purpose of illustration only. In the appended specification and claims all percentages are percentages by weight unless otherwise stated.